Heterocyclizations of Di- and Tricarbonyl Indole Derivatives. Synthesis of β-Carbolines, 3H-[1,2,5]Triazepino-[5,4-a]indol-4(5H)-one, and 5,10-Dihydro[1,2]diazepino-[4,5-b]indol-4(3H)-one

Abstract

A synthetic approach to β-carbolines has been proposed on the basis of heterocyclization of ethyl 2-(2-benzoyl-1H-indol-3-yl)acetate with N-methylformamide or ammonium acetate. Hydrazine hydrate proved to be inefficient in this reaction. The heterocyclization of dimethyl 2,2′-(2-benzoyl-1H-indole-1,3-diyl)diacetate with ammonium acetate selectively afforded 2-(3-hydroxy-1-phenyl-9H-pyrido[3,4-b]indol-9-yl)acetamide. Treatment of dimethyl 2,2′-(2-benzoyl-1H-indole-1,3-diyl)diacetate with hydrazine hydrate, followed by acid-catalyzed heterocyclization, gave methyl 2-(4-oxo-1-phenyl-4,5-dihydro-3H-[1,2,5]triazepino[5,4-a]indol-11-yl)acetate or 2-{4-oxo-1-phenyl-4,5-dihydro[1,2]diazepino[4,5-b]indol-10(3H)-yl}acetohydrazide, depending on the conditions.